Seedsman CBD 30:1 First time

Ive just started this week on friday with a day old seedling, planted in a rockwool cube that was PHed down to 5.5, the seedling was started by soaking in a glass of PHed water for 24 hours till the taproot started to show, whereafter it was inserted taproot down into the hole of the rockwool cube, kept moist and this tiny little seedling showed up. My plan for this plant is to use it as a mother plant and take clones every two weeks to use for flowering, as clones are taken I will update and show their progress. I am growing all my plants in a home built RDWC Bubbleponics hybrid system that I will use for all of my future production, I love the explosive growth that this system gives for relatively low maintenance and high yields. I typically use all grow techniques except 12-12 from seed and will be doing a sea of green with clones on a perpetual basis as money allows, I'm doing this on an extremely small budget.

Ok so im doing ok so far but ive run into an issue with heat, it has become winter here in south Africa, which means that for us its quite cold and I've had to get a heater for the room, I've got it running on a thermostat keeping it at 25c all day long, we went away for a few days and came back to see this weird thing going on with the leaves, there was new growth which I topped that looked to have nutrient burn on the new leaf growth and on the older leaves it looked like old peoples hands, all wrinkled and not looking great... any ideas on what it could be?